This invention relates to improvements in power trains, especially for use in motor vehicles. More particularly, the present invention relates to improvements in power trains of the type wherein a rotary output member of a prime mover, such as the crankshaft or the camshaft of the engine in a motor vehicle, serves to transmit torque to the rotary input member of a driven unit (e.g., to the input shaft of the change-speed transmission in the power train of a motor vehicle) by way of a friction clutch. Still more particularly, the present invention relates to improvements in means for engaging and/or disengaging the friction clutch to thus respectively establish and interrupt the flow of torque between the prime mover and the driven unit.
In many presently known power trains for use in motor vehicles, the clutch is selectively engageable and disengageable by a fluid-operated coupling system which can include a master cylinder and a slave cylinder having a piston reciprocable in a cylinder or housing and operatively connected with a component part (e.g., a diaphragm spring (also called Belleville spring) or another suitable energy storing device of the clutch) by way of a release bearing. Reference may be had, for example, to commonly owned U.S. Pat. No. 5,632,706 granted May 27, 1997 to Kremmling et al. for “MOTOR VEHICLE WITH ELECTRONIC CLUTCH MANAGEMENT SYSTEM”.
It is also known to install the slave cylinder in such a way that it is coaxial with the input shaft of the transmission. Reference may be had, for example, to German patent No. 44 27 942 A1 which discloses a power train wherein the cylindrical housing of the slave cylinder is affixed (e.g., by means of fasteners) to the housing or case of the change-speed transmission. Thus, in order to assemble the power train, the clutch must be mounted on the output member of the prime mover (e.g., on the camshaft or crankshaft of the internal combustion engine), and the clutch engaging/disengaging means (such as the housing and the piston of the slave cylinder) must be mounted on the transmission. The establishment of actual connection between the clutch and the engaging/disengaging means therefor must be carried out in a next-following step. This creates problems when the output member of the prime mover must be realigned with the input member of the change speed transmission, an undertaking which must be carried out rather frequently in the power trains of motor vehicles. Furthermore, it is normally necessary to employ a self-centering system for the clutch release bearing in order to compensate for or to counteract the misalignment of the output member of the prime mover and of the input member of the transmission.
The piston of the slave cylinder in the above outlined conventional power trains is movable axially of the housing of the slave cylinder and, in order to change the condition of (e.g., to disengage) the friction clutch, normally acts axially upon the energy storing element (such as the aforementioned diaphragm spring) of the friction clutch. The body of fluid in the slave cylinder, as well as the piston of this cylinder, react against such housing (i.e., against the case of the change-speed transmission) whenever the piston is to move axially toward the prime mover in order to change the condition of (e.g., to engage) the clutch. In addition, the transmission case must also withstand the force with which the energy storing element of the clutch resists deformation by the piston of the slave cylinder. Otherwise stated, when the clutch of the just described conventional power train is to change its condition (e.g., to be disengaged) as a result of axial movement of the piston relative to the housing of the slave cylinder in response to admission of pressurized fluid into the housing, the flow of power takes place from the energy storing element of the clutch, through the piston of the slave cylinder, through the body of pressurized fluid in the housing of the slave cylinder, through the the just mentioned housing, through the transmission case, through the housing of the engine or another suitable prime mover, through suitable engine supporting or bearing means, and on to the rotary output member (such as the aforementioned crankshaft or camshaft) of the engine. Therefore, all of the just enumerated power transmitting and withstanding parts must be designed (such as dimensioned, configurated and or made of special materials) with a view to reliably withstand the developing forces during the useful life of the power train. Another part which must withstand at least some of the aforediscussed power or force is the housing or cover of the friction clutch; the latter must withstand the forces being transmitted by the energy storing element (hereinafter called spring or diaphragm spring) of the friction clutch.
It is well known that the crankshaft or another rotary output member of the engine in the power train of a motor vehicle invariably performs undesirable stray (such as wobbling and/or axial) movements which must be taken up by the slave cylinder and at least a percentage of which is transmitted from the slave cylinder to the means (such as a pipe and a master cylinder) which is provided to supply pressurized fluid (such as oil or another hydraulic fluid) to the chamber or chambers of the housing (cylinder) of the slave cylinder. The stray movements of the slave cylinder are felt by the operator of the vehicle, namely as vibrations of the clutch pedal, and are or can constitute a cause of considerable discomfort.
If the just discussed operator-controlled combined mechanical and fluid-operated clutch actuating (such as disengaging) system is replaced with an automatic or automated system, e.g., with a system which employs an electrical or electronic actuator in lieu of the fluid-operated master cylinder, the power train exhibits other types of undesirable characteristics such as and especially in connection with (a) reliable and acceptable determination (timing) of the engagement and disengagement of the friction clutch, (b) prolonged transmission of acceptable or optimal torque, and/or others.
Proposals to overcome the above-enumerated problems (such as vibration) in power trains employing manually or automatically operated clutch engaging/disengaging systems include the utilization of various types of antivibration units (also called vibration dampers, vibration filters and antivibration assemblies). Reference may be had, for example, to commonly owned British patent application Serial No. 2 348 259 A wherein the antivibration units are called “damping devices”. A drawback of presently known antivibration units is that they are not only bulky, complex and expensive but that they are also far from being a reliable and versatile means for solving the above-enumerated problems. They normally rely upon a throttling action, i.e., they are intended to throttle the undesirable stray movements and/or dampen the noises, they establish space-requiring dead volumes for bodies of fluid and/or they employ expensive materials and/or resort to complex and expensive procedures for the making of several parts in the force transmitting system between the actuator (such as a fluid-operated or electrical actuator means) and one or more parts (such as a diaphragm spring or another resilient element) of the friction clutch.